This application claims priority to an application entitled xe2x80x9cAAL2 Processing Device and Method for ATM Networkxe2x80x9d filed in the Korean Industrial Property Office on Nov. 13, 1998 and assigned Ser. No. 98-48578.
1. Field of the Invention
The present invention relates generally to an ATM (Asynchronous Transfer Mode) network, and in particular, to an AAL2 (ATM Adaptation Layer 2) processing device and method.
2. Description of the Related Art
A reference model of a B-ISDN (Broadband Integrated Services Digital Network) protocol, as shown in FIG. 1, is comprised of a vertical layer structure (protocol stack) including a physical layer, an ATM layer, ATM adaptation layers (AALs) and higher layers; and a horizontal plane structure including a user plane, a control plane and a management plane.
The AAL layer, which is interposed between the ATM layer and the higher layers, segments data information from the higher layers by the proper length for the cell structure. There are four different AAL protocols: AAL1, AAL2, AAL3/4 and AAL5. As is well known in the art, the AALs have a shorter and simple connection setup time during software processing, as compared with the ATM layer. Therefore, the ML layers in-between the ATM layer and the higher layers are widely used. Active research has been made on AAL1, AAL3/4 and AAL5, establishing the standard of a PDU (Protocol Data Unit) format in the respective layers. More recent research has been carried out on AAL2. As a result, an AAL2 CPS-PDU (AAL2 Common Part convergence Sublayer-PDU) format was established as a standard in ITU-T Recommendation I.362.2(D) in October, 1997. However, research on a method for controlling and managing the AAL2 CPS-PDU format is currently being carried out and will be completed by 2000.
AAL2 enables effective use of limited bandwidth by using multiplexing, which is also used by AAL1 and AAL3/4, and is fundamentally different from AAL5, which does not use the multiplexing concept. AAL1 is for carrying a circuit-based frame (for example, a T1 or E1 frame), not for multiplexing channels. In addition, unlike the circuit network-based AAL1, AAL2 is based on the ATM network. Further, unlike AAL3/4, which is only good for data service, AAL2 can service on average 3 or 4 additional subscribers on the basis of a single virtual circuit (VC) i.e., on the basis of one line, so that it is possible to more easily transmit real-time information having a short length. In general, a great deal of cells are transmitted through a single VC, and in a single cell, there can be one or more AAL2 packets. AAL3/4 is not good for carrying voice traffic because of transmission efficiency issues.
The AAL2 CPS-PDU format can be useful when transmitting multiple channels by multiplexing the channels into one ATM connection. In the ATM network, when transmitting real-time data (e.g., voice) having a short length, a transmission delay problem may occur due to loss of bandwidth or failure to maintain the real-time properties of the voice data. This problem can be solved by multiplexing the multiple channels into one ATM connection. In other words, by using the current AAL2 CPS-PDU format, it is possible to prevent a loss of the bandwidth or transmission delay when transmitting real-time information having a short length. As stated above, however, currently, there is no proposed method for controlling and managing the AAL2 CPS-PDU format.
It is, therefore, an object of the present invention to provide a device for preventing loss of bandwidth or transmission delay when transmitting real-time data having a short length in an ATM network.
It is another object of the present invention to provide a device for controlling and managing the AAL2 CPS-PDU format in an ATM network.
To achieve the above objects, there is provided an AAL2 processing device comprising an AAL2 synchronizer for receiving an AAL2 cell in which at least one AAL2 packet is multiplexed, and detecting a start point of each packet to synchronize the packet; an AAL2 switch for switching the synchronized packet according to routing information provided during call setup; and an AAL2 formatter for multiplexing the switched packet according to ATM connections, and generating an output AAL2 cell having the same format as the input AAL2 cell. Further, the AAL2 processing device comprises a CID (Channel Identification) changer interconnected between the AAL2 synchronizer and the AAL2 switch, for determining whether there are packets to be switched to the identical ATM connection at the same time out of the packets to be switched by the AAL2 switch by using the cell routing information, and changing, when there are such packets, the CIDs of the packets so that the CIDs of the packets are not identical to each other.